Does anyone know why Boeing designed the 737 without any landing gear doors for the main landing gear? Its kind of cool seeing the landing gear in its up position from the ground sometimes, and also doesnt it pose some type of safety hazard without having landing gear doors for the main gear on the 737? Doesnt the cold freezing atmosphere conditions at 25,000+ feet have any type of hazards for the main gear?

Quoting Propilot83 (Thread starter):Does anyone know why Boeing designed the 737 without any landing gear doors for the main landing gear?

a. Complexity issues and weight savings associated with the doors.

Quoting Propilot83 (Thread starter):doesnt it pose some type of safety hazard without having landing gear doors for the main gear on the 737? Doesnt the cold freezing atmosphere conditions at 25,000+ feet have any type of hazards for the main gear?

b. Even if there were landing gear doors, the space where the wheels are is not heated. Hence on a four hour cruise the temperature inside the wheel well is the same as not having the door open. Hence there is no problem. I'm sure somewhat would have noticed one in 40+ years of service.

Kleinsim has it right. MLG doors add complexity and weight. And they don't shield the tires from cold cruising temperatures anyway.

The 737 was designed in the 60s, and was initially intended for relatively short flights. At the time, whatever aerodynamic penalties for a door-less MLG were outweighed by the weight and added complexity MLG doors added to the overall design. Over the years, Boeing has had the opportunity to add MLG doors. But because even the relatively long-range newest 737s haven't incorporated this added complexity, it's safe to say that it doesn't buy operators enough efficiency to be worth while in cost, maintenance, or efficiency.

Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.

Quoting Propilot83 (Thread starter):Doesnt the cold freezing atmosphere conditions at 25,000+ feet have any type of hazards for the main gear?

It is less a problem for the tires as it is for all the components in the wheel well. On a 737, real estate is tight, so most of the hydraulic and flight control systems components are in the wheel well. It is a very harsh environment for those components. Temperatures get as low as -65C. Air pressure obviously is only a few PSI. Worst of all, tire spray from runway deicing fluids and any other contamination on a runway gets kicked up in the wheel well which causes corrosion. It is very difficult on valves, pumps and other components. Tires, wheels, and landing gear are more structural components that don't have the tight tolerances and moving parts that make them as susceptible to those conditions.

Quoting Propilot83 (Thread starter):Does anyone know why Boeing designed the 737 without any landing gear doors for the main landing gear?

Saves weight and reduces complexity. With the aerodynamic hub cap, there isn't that much of a drag penalty.

Quoting Speedracer1407 (Reply 2):
The 737 was designed in the 60s, and was initially intended for relatively short flights. At the time, whatever aerodynamic penalties for a door-less MLG were outweighed by the weight and added complexity MLG doors added to the overall design.

There have been options studied to reduce drag like partial wheel covers, but finding a way for them to fold out of the way when the gear is down is quite complex on a plane as low to the ground. The weight penalty is also a big hit that is hard to justify with drag reductions.

If you have never designed an airplane part before, let the real designers do the work!

Thanks for the info guys, WOW! I didnt think adding main landing gear doors would cause so much more weight and drag for the plane in flight. Yea, it also makes sense that the plane is real low to the ground to have landing gear doors for the main gear!

The 737 originally had an inflating seal which filled the gap around the outer mainwheel tyre in the stowed position. This proved maintenance-hungry and didn't make much difference to the drag, so was replaced by the multi-petal rubber flap system which seals the gap ever since.

The Cessna 210 originally had main gear doors, but later models didn't for the same reasons as on the 737.

Actually each MLG on the B737 has a Outboard ,mid & Inner Landing gear door,mechanically attached to the gear & operated by it.
True there is no door covering the exposed wheel & a hub cap is provided for aerodynamic reasons.
Considering the weight saved & non use of sequence valves and added components,this MLG construction has served well for the B737.
regdsMEL.